U.S. Pat. No. 4,736,144 disclosed by the same inventor of this application includes an automatic door which is driven by a motor and speed sensor and is controlled by a servo-controlled safety protection device. However, the servo-controlled protection circuit requires more labors for the assembly, test and inspection when producing the control circuit and may increase operation and maintenance problem when used.
Even Yoshida, et. al disclosed a control apparatus for an automatic door with a minimum error in a detected door position in their U.S. Pat. No. 4,529,920 including a main control 12 having a door position measuring means 23, a state sequencer 24, a door stroke setter 25, two channels for handling opening and closing modes of operations and a gate circuit 29. Such a complex circuit may still increase operation and maintenance problems.
It is therefore expected to invent an automatic door including a software of microprocessing control program in cooperation with a servo-control network for automatically controlling an automatic door.